Along with endoscopes for medical and non-medical technical applications, whose viewing direction is parallel to the longitudinal axis of the shaft of the endoscope, endoscopes with other fixed viewing directions were developed from an early time. The viewing direction of an endoscope is always understood here and in the following text to mean the direction, looking from the distal end of the endoscope, in which an object is situated that appears in the center of the image captured by the endoscope. However, with many applications a fixed viewing direction is a disadvantage. In the worst case, the endoscope must be repeatedly replaced, for example during a medical procedure. In such cases it is advantageous to use an endoscope with a viewing direction that can be adjusted or displaced in situ.
A swing prism endoscope comprises on the distal end a pivotable prism, on whose border surfaces light impinging into the endoscope is broken up and reflected before being conveyed to the proximal end of the endoscope, for example by means of a rod lens system. The viewing direction can be adjusted by swinging the prism around an axis perpendicular to the longitudinal axis of the endoscope shaft.
Conventional swing prism endoscopes, however, have an unsatisfactory viewing direction range. If the viewing direction range is intended to include a viewing direction parallel to the axis of the endoscope shaft (zero degrees), for some time now only a small viewing direction range could be achieved, with less than 45 degrees between its extreme viewing directions. A large viewing direction range, with 75 degrees or more between its extreme viewing directions, for some time has included at best, for example, viewing directions of 45 to 120 degrees or 15 to 120 degrees or 10 to 115 degrees to the axis of the endoscope shaft.